Device for extracting short-circuiting wedges when switching in an electrolysis cell for the production of aluminum

ABSTRACT

Extraction device designed to extract a short-circuiting wedge inserted between two conductors to take an electrolysis cell offline. The extraction device includes a means of gripping said wedge and at least one jack directed vertically and including a body and a piston stem.
         said body (or stern) being interdependent with at least one horizontal support face directed downwards and laid out so that, when said extraction device is placed above said wedge to extract it, the upper horizontal face of each conductor is in line with one horizontal support face,   b) said stem (or said body) being connected to said means of gripping said wedge, so that, when said jack is actuated to extract the wedge, said jack exerts opposing forces on said conductors and said wedge, tending to separate them.

The invention relates to the field of aluminum production using igneous electrolysis by means of the Hall-Héroult process. It concerns devices for the electrical connection of electrolytic cells for the production of aluminum by igneous electrolysis. It more particularly relates to equipment which is used during the restarting operation of a cell taken temporarily out of service, an operation also called “switching-in”, and which makes it possible to remove short-circuiting wedges placed between the cathode assembly of said cell and the cathode assembly of the adjacent upstream cell. In the following, such equipment will be referred to as a “wedge extraction device” or “extractor”.

Aluminum is produced industrially by igneous electrolysis, using the well-known Hall-Héroult process, in electrolysis cells. The plants contain a great number of electrolysis cells laid out in line, in buildings called electrolysis halls or rooms, and electrically connected in series using connecting conductors, in order to make the best use of the floor area of the plants. Each electrolytic cell comprises a pot provided with a cathode assembly and an anode system. The pot comprises a steel pot shell, elements of refractory material lining and a cathode assembly located at the bottom of the pot, formed by the juxtaposition of carbonaceous blocks in which are sealed metal bars whose ends protrude from the pot shell. Each pot also comprises an anode system formed by at least one rigid beam, which supports one or more horizontal conducting bars, called an “anode frame”, on which are fixed the anode hanger rods made of carbonaceous material which are partially immersed in the electrolytic bath.

The cells are generally laid out so as to form two or more parallel lines which are electrically linked to each other by end conductors. Conventionally, electric current flows from the cathode of an upstream cell towards the anode of a downstream cell. The connecting circuit between two successive cells includes a circuit carrying the electrolysis current, made up of cathode collectors connected both to the cathode outputs of a cell of a given row (n) and to “anode risers”, themselves connected to the rigid beam and the anode frames of the adjacent downstream cell, of row (n+1).

From time to time, one or more cells of a series must be shut down. This shutdown is performed by connecting the cathode collector of a given cell to the connecting conductor which connects the cathode outputs of the adjacent upstream cell to the “anode risers” which power the anode frame of said cell. Connection is made via a plurality of conducting wedges, typically made of aluminum, such as those mentioned in patent FR 2.583.069 (see FIG. 8, element marked 12): in such a configuration, the cathode collector of the cell and the connecting conductor between the cathode of the upstream cell and the anode of said cell appear locally as two conductors with a substantially rectangular section, each of which has at least one horizontal upper face and one substantially vertical face, the substantially vertical face of one conductor being placed opposite that of the other, the two substantially vertical faces thereby delimiting an air-gap designed to receive a short-circuiting wedge, itself including two substantially parallel faces, which converge slightly towards the bottom when the wedge is placed so as to occupy said air-gap.

In order to shut down the cell, the wedges must be inserted between the conductors in order to provide a contact surface that gives as low as possible an electrical resistance. In practice, to ensure a good electrical contact, these wedges are introduced into the air-gap between the conductors, while these are themselves retained by bolted ties.

To switch in the cell, said wedges must be withdrawn, so as to isolate said conductors from each other, the current flowing from the upstream cell passing once more through the anode risers to power the anode frame of the adjacent downstream cell. To remove the wedges without having to supply too great a force, it is in general necessary to at least partially unbolt said ties. The wedges are then pulled to the top so that they leave the air-gap engineered between the conductors.

Until now fitting and removing these wedges required tricky human intervention, involving either shutting down the series for the time necessary for the operation, which is detrimental to the output of the series, or, preferably, an intervention of very limited duration. If the wedges are withdrawn without the series being shut down, and as all the wedges cannot be removed instantaneously, the intensity of the current which flows in the wedges that are still in place increases gradually, causing them to significantly overheat, so that the last wedges removed may reach high temperatures. A high wedge temperature may have detrimental consequences, such as having to exert a higher extraction force because they have dilated, or leading to significant damage to the contact surfaces. So the intervention must be as short as possible to limit overheating of the last wedges to be removed.

Moreover, safety requirements mean that operators have to remain at ground level, in particular when they are working on said wedges. Around current electrolytic cells, passages are arranged to facilitate various work on the cell. These passages are roughly on the same level as the surface of the bath. For safety reasons, the cathode collectors and the connecting conductors are located below these passages. The conductors and the air-gaps designed to receive the wedges are therefore laid out below these passages but they must be accessible from these passages, during the operations necessary for momentarily shutting down or switching in the cell.

To save time during these operations, it has been attempted to remove the wedges using a hoist placed on a traveling crane moving in the electrolysis hall, above the cells. To achieve this, short-circuiting wedges provided with ladle pins have been used and the hoist was provided with a U-shaped sling designed to be hung from the wedge pins. The hoist made it possible to develop significant forces, typically about 10 tons, but these were insufficient if the ties were not at least partially unbolted beforehand. This led to a significant waste of time because the ties could only be unbolted from ground level, with a long-handled tool with only limited rotation possibilities. In addition, when, in spite of the force transmitted, the wedge still adhered to the conductors, the hoist ultimately lifted up anyway, entraining and damaging the conductors. Lastly, such a practice raised major safety issues, because the wedges, which have a certain mass, typically a few tens of kilograms, were expelled along a more-or-less controlled upward trajectory, and likely to pass near the operators.

The applicant has developed a process for extracting wedges which does not have the disadvantages referred to above, in which an extractor is used which acts on the wedges without any need to unbolt the ties, exerts a significant effort during wedge extraction without leading to the least risk of damage to said conductors and, finally, makes it possible to control the ejection trajectory of said wedges.

A first subject according to the invention is an extraction device designed to extract a short-circuiting wedge, said wedge having been inserted between two conductors to take an electrolytic cell off line, each conductor having at least one upper horizontal face and one substantially vertical face, the substantially vertical face of a conductor being placed opposite that of the other, the two substantially vertical faces thereby delimiting an air-gap designed to receive said short-circuiting wedge, itself comprising two substantially parallel faces, which converge slightly to the bottom when said wedge is placed so as to occupy said air-gap, said device including a means of gripping said wedge and characterized in that it also includes at least one jack directed vertically comprising a body and a piston with which is associated a piston stem,

-   -   a) said body (or said stem) being interdependent with at least         one horizontal support face which is directed downwards and laid         out so that, when said extraction device is placed above said         wedge to extract it, the upper horizontal face of each conductor         is in line with said horizontal support face,     -   b) said stem (or said body) being connected to said means of         gripping said wedge, so that, when said jack is actuated to         extract the wedge, said jack exerts opposing forces on said         conductors and said wedge, tending to separate them.

By using the wedge extraction device according to the invention, an electrolytic cell can be switched in by isolating the conductors, together with the cathode elements of two adjacent cells, from each other, without damaging them: the force compensating for the force which tends to separate the wedge from the conductor is the resultant of forces exerted directly on the upper horizontal face of each conductor, which makes it possible to prevent the conductors from lifting up and becoming damaged, should the extraction force be insufficient to detach the wedge from the conductors. This device, able to provide forces greater than those of prior art without damaging the conductors, is all the more appropriate as the wedge is held strongly between two conductors retained by ties.

As previously indicated, the two conductors opposite each other are:

-   -   a first conductor, which is a connecting conductor between the         cathode output of the cell directly upstream and the anode riser         which supplies the anode frame of said cell,     -   a second conductor, which is a cathode collector element of said         cell.

The extraction device according to the invention includes at least one jack that is placed so that it can, when actuated, exert opposing forces on the wedge and on at least one conductor. Each of the two parts of the jack, which are mobile in relation to each other (body and stem), may be associated either with the wedge or with the conductors. The first part of the jack (the body or the stem) is interdependent with at least one horizontal support face designed to come in line with the upper horizontal face of a conductor. The second part of the jack (the stem or the body) is connected to the means of gripping the wedge, at least temporarily, when the jack is actuated to extract the wedge. In other words, this second part of the jack may be mobile in relation to said means of gripping in certain phases of use of the extraction device but it must come into contact with this means of gripping and entrain it when the jack is actuated in order to exert the separating forces.

The means of gripping the wedge advantageously includes a fixing part on which means of fixing are fastened, working in conjunction with complementary means of fixing engineered on the wedge, preferably on the top part of the wedge which is designed to remain above the air-gap of the conductors when the wedge is inserted into it and which is therefore more easily accessible. For example, on the top part of the wedge at least one substantially horizontal bore is engineered, designed for a locking axle, interdependent with the fixing part, to pass through it. The locking axle(s) is (are) actuated by one or more auxiliary actuators, which are themselves fixed to said fixing part and which cause said axles to move so that they can fit into said bore so as to grip the wedge.

In practice, the conductors are placed opposite each other so that the wedge is placed vertically and the extractor can therefore be set up at the level of the wedge to be extracted using a transporting and lifting device, of the traveling crane/carriage/hoist type. But the invention remains significant if the pair of horizontal and vertical directions mentioned is replaced by any pair of perpendicular directions, each wedge needing to have an upper face that is perpendicular to the direction of the air gap which separates them, the handling device designed to place said device in line with the wedges obviously being adapted to such a frame of reference.

The extraction device according to the invention includes at least one jack with the characteristics specified above. This jack may be an electric jack, typically powered by a circuit with a variable speed drive, but, preferably, it is a hydraulic actuating cylinder, because the latter, for a given size, is able to exert a greater force. Advantageously, the hydraulic actuating cylinder(s) is (are) powered by the same hydro-electric unit, which is preferably mounted on said extraction device or the handling device of said extraction device.

In a preferred embodiment of the invention, said extraction device also includes an actuator designed to raise the unit including the wedge, the means of gripping the wedge and the jacks, as soon as the wedge has been extracted, i.e. as soon as it is no longer held in place by the conductors. This actuator acts as an ejector: the unit including the wedge and the means of gripping the wedge must be removed so that the wedge can completely leave the air-gap between the conductors opposite each other as quickly as possible, at a speed significantly higher than that of the stem of a hydraulic actuating cylinder. For the unit including the wedge and the means of gripping, it is attempted to find as high an ejection speed as possible because this makes it possible to limit the risk of an electric arc appearing as the wedge rises.

Advantageously, said actuator, also called an ejector, is a pneumatic jack. Advantageously, the means of gripping the wedge is interdependent with the stem (or the body) of said ejector and the stem travel of said ejector is long enough to allow said wedge to completely leave the conductor air-gap.

In a preferred embodiment, the support jack(s) and the ejector operate simultaneously. There is then no need to synchronize the actions of the jack(s) and the ejector: as the extraction force exerted on the wedge, provided by the jacks, is substantially greater than the force supplied by the ejector, it is applied only until the wedge breaks away from the conductors, at which point only the raising force of the ejector is operative.

Advantageously, said extraction device includes a frame on which said ejector is fixed. Said frame includes means of fixing, so that it can be handled by transport and lifting means. Typically, the means used for transporting and lifting said extraction device are an association of traveling crane, carriage and hoist. To extract a wedge, the device is placed, using said transport and lifting means, in line with the conductors and it is placed in such a way that at least one horizontal support face rests on an upper horizontal face of a conductor. During extraction, the extraction device may or may not be held by the transport and lifting means.

Advantageously, said frame is provided with means of centering which make it possible to guide said extraction device during its vertical move downwards towards a predefined position in relation to said conductors, the support faces being placed in line with the upper horizontal faces of said conductors.

Advantageously, said frame also includes fairing which delimits the space in which the unit including the wedge and the means of gripping the wedge must move after said wedge has been extracted and which provides protection for the operators working near the extractor against the extracted moving parts.

Another subject according to the invention is an extraction process for short-circuiting wedges used when switching in an electrolytic cell temporarily taken off line, consisting in removing the short-circuiting wedges which were inserted between two conductors to take said electrolytic cell off line, the first conductor being associated with the cathode assembly of said cell and the second conductor being associated with the cathode assembly of the adjacent upstream cell, each conductor having at least one upper horizontal face and a substantially vertical face, the substantially vertical face of a conductor being placed opposite that of the other, the two substantially vertical faces therefore delimiting an air-gap designed to receive said short-circuiting wedge, itself including two substantially parallel faces, which converge slightly to the bottom when said wedge is placed so as to occupy said air-gap, said process being characterized in that the device according to the invention is used to extract said wedge.

Advantageously, as work needs to be carried out as quickly as possible to limit heating of the last wedges to be removed, several devices according to the invention are used simultaneously to extract some or all of the wedges which were fitted when taking an electrolytic cell off line.

FIG. 1 is a schematic cross-sectional view of a pot tending machine in a typical electrolysis hall for the production of aluminum.

FIG. 2 is a schematic view of the layout of the connecting conductors between two neighboring cells.

FIGS. 3 a and 3 b schematically illustrate a particular embodiment of the wedge extraction device according to the invention. FIG. 3 a shows said extraction device when it is fitted to the conductors, at the level of the wedge to be extracted. FIG. 3 b shows said extraction device when the wedge has been extracted and is still in place, resting against the conductors, at the level of the wedge which has just been extracted.

Electrolysis plants designed for aluminum production include one or more electrolysis halls. The electrolysis hall (1) illustrated in FIG. 1 comprises electrolysis cells (2) and a pot tending machine (5). The electrolysis cells (2) are normally laid out in row or lines, each row or line typically comprising over a hundred cells. The cells (2) are laid out so as to leave an aisle throughout the length of the electrolysis hall (1). Cells (2) include a series of anodes (3) provided with a metal stem (4) for fixing the anodes and connecting them electrically to a metal anode frame (27). Each cell (2) comprises a cell provided with a cathode assembly (22) and an anode system (26). The cell comprises a steel pot shell and elements of refractory material lining. The cathode assembly (22) located at the bottom of the cell, is formed by the juxtaposition of carbonaceous blocks in which are sealed metal bars whose ends (21) protrude from the pot shell and are connected to each other by a cathode collector (23). The connecting circuit between two successive cells (2. (n−1) and 2.n) includes a circuit for carrying the electrolysis current where the cathode collector (23. (n−1)) is connected to the cathode outputs (21. (n−1)) of a cell in a given row (2. (n−1)) and also to anode risers (28.n), themselves connected to the anode frames (27.n) of the adjacent downstream cell (2.n).

From time to time, one or more cells of a series must be shut down. This shutdown is performed by connecting the cathode collector (23.n) of a given cell (2.n) to the connecting conductor which connects the cathode collector (23(n−1)) of the adjacent upstream cell (2.(n−1)) to the anode risers (28.n) which power the anode frame of said cell. Connection is made via a plurality of conducting wedges (20), typically made of aluminum, inserted by force into different places where the two conductors have two substantially vertical faces opposite each other. To switch in the cell, all the wedges must be removed in as short a time as possible. The device according to the invention makes it possible to remove the wedges one by one. It can be moved quickly in line with each wedge and can exert a large extraction force making it possible to detach each wedge from the conductors.

Example of an Embodiment (FIGS. 3 a and 3 b)

The extraction device (30) illustrated in FIGS. 3 a) and b) is designed to extract a short-circuiting wedge (20), which was inserted between two conductors (24 and 25) to take an electrolytic cell off line. The first conductor (24) is a connecting conductor between the cathode output (23.(n−1)) of the cell directly upstream and the anode riser (28.n) which supplies the anode frame (27) of said downstream cell (2.n). The second conductor (25) is a portion of the cathode collector (23.n) of said downstream cell (2.n). Each conductor (24, 25) has at least one upper horizontal face (240, 250) and a substantially vertical face (241, 251). The substantially vertical faces (241, 251) are placed opposite each other, therefore delimiting an air-gap designed to receive said short-circuiting wedge, itself including two substantially parallel faces (204, 205), which converge slightly downwards.

The extraction device (30) includes a means of gripping (31) said wedge and a jack (32) directed vertically and including a body (320) and a stem (321). Body (320) is interdependent, via a hollow intermediate part (33), with a horizontal support face (335) which is directed downwards and laid out so that, when said extraction device is placed above said wedge to extract it, the upper horizontal face (240, 250) of each conductor (24, 25) is in line with the horizontal support face (335). The stem (321) is connected to the means of gripping (31) wedge (20), so that when jack (32) is actuated to extract the wedge, said jack exerts opposing forces on the conductors (24, 25) and on the wedge (20), tending to separate them. Jack (32) is a double-acting hydraulic actuating cylinder, powered by a hydraulic unit via a circuit arranged so that said extraction is carried out when the chamber on the piston side (322) is supplied.

In this embodiment, the body (320) of the jack (32) has a lower horizontal face (325) which is in contact with the upper horizontal face (331) of the intermediate part (33) when the extraction device is placed on the conductors in order to extract a wedge. When jack (32) is operated, a vertical force is exerted on the upper horizontal face (331) of the intermediate part (33) and is transmitted to the conductors via the lower horizontal face, which acts as a horizontal support face (335), itself put into contact with the upper horizontal faces (240, 250) of the conductors (24, 25).

Stem (321) is hollow, passing right through via an axial bore (3211) through which an axle (40) interdependent with the means of gripping (31) of the wedge can slide. Said axle (40) interdependent with the means of gripping is provided with a shoulder (41) which acts as a stop to the axial movement of the stem (321): when the jack is operated, oil under pressure fills the chamber on the piston side (322), which entrains the stem (321) upwards. The end (3210) of stem (321) comes into contact with the shoulder (41) of axle (40), so that said jack (32) acts on the axle and exerts a force upwards on said gripping device (31).

To make it easier to extract, wedge (20) and said extraction device (30) are provided with means of gripping working in conjunction with each other. The extraction device (30) includes, as a means of gripping the wedge, a fixing part (313) in the general shape of an upside-down U, the two legs of the U, provided with bores being, in order to extract the wedge, placed on either side of the upper end of the wedge, and two ladle pins (311, 312) placed so that they are located, aligned horizontally, on either side of the wedge (20). The top part of wedge (20), designed to remain above the air-gap of the conductors, has a horizontal bore (201) passing through the entire thickness of the wedge. Each ladle pin (311, 312) can be actuated by a jack (315, 316) which makes it possible, by means of an appropriate connecting stem assembly, to insert said ladle pin inside the bore (201) of the wedge and the bore of the leg of the fixing part associated with said ladle pin, in order to grip the wedge. The fixing part (313) is fixed to the lower end of the vertical axle (40).

The intermediate part (33) also acts as fairing which provides protection for the operators working near the extraction device against the extracted moving parts.

The extraction device (30) also includes an actuator (50) designed to raise the unit including the wedge, the means of gripping the wedge and the jacks, as soon as the wedge has been extracted, i.e. as soon as it is no longer held in place by the conductors. This actuator is a pneumatic jack (51). The means of gripping (31) the wedge is fixed to the lower end of the axle (40), which is itself an extension of the stem (52) of actuator (50). During extraction, the jack (32) and the actuator (50) operate simultaneously: as the extraction force exerted on the wedge, provided by the jack (32), is substantially greater than the force supplied by the actuator (50), it is applied only until the wedge breaks away from the conductors, at which point only the raising force of the actuator (50) is operative.

The extraction device (30) also includes a frame (60) onto which is fixed said actuator (50). This frame is illustrated schematically here, united with the intermediate part (33) which makes up its bottom part. Said frame includes means of fixing (not shown), so that it can be handled by transport and lifting means. 

1. Extraction device designed to extract a short-circuiting wedge, said wedge having been inserted between two conductors to take an electrolytic cell off line, each conductor having at least one upper horizontal face and one substantially vertical face, the substantially vertical face of each conductor being placed opposite the substantially vertical face of the other conductor, the two substantially vertical faces thereby delimiting an air-gap designed to receive said short-circuiting wedge, said wedge comprising two substantially parallel faces, which converge slightly to a bottom of said wedge when said wedge is placed so as to occupy said air-gap, said device including a means of gripping said wedge, wherein said device includes at least one jack directed vertically and comprising a body and a piston associated with a piston stem, wherein: a) one of said body or said stem is interdependent with at least one horizontal support face which is directed downwards and configured so that, when said extraction device is placed above said wedge to extract the wedge, the upper horizontal face of each conductor is in line with the horizontal support face, and b) the other of said stem or said body is connected to said means of gripping said wedge, so that, when said at least one jack is actuated to extract the wedge, said at least one jack is configured to exert opposing forces on said conductors and said wedge, tending to separate said conductors and said wedge.
 2. Extraction device according to claim 1 characterized in that said means of gripping includes a fixing part onto which are attached means of fixing working in conjunction with means of fixing engineered in the top part of the wedge which is designed to remain above the air-gap of the conductors when the wedge is inserted into the air gap.
 3. Extraction device according to claim 1 characterized in that said at least one jack is a hydraulic actuating cylinder.
 4. Extraction device according to claim 1 characterized in that the device also includes an actuator designed to raise, as soon as the wedge is no longer held by the conductors, a unit including the wedge, the means of gripping said wedge and said at least one jack so that said unit comes out of said air-gap between said conductors.
 5. Extraction device according to claim 4, characterized in that said actuator is a pneumatic jack.
 6. Extraction device according to claim 4, characterized in that said at least one jack and said actuator are configured to operate simultaneously during the extraction of said wedge.
 7. Extraction device according to claim 6 characterized in that the device also includes a frame onto which is fixed said actuator, said frame including means of fixing, so that said frame can be handled by transport and lifting means.
 8. Extraction device according to claim 7, characterized in that said frame is provided with means of centering configured to guide said extraction device during vertical movement downwards towards a predefined position in relation to said conductors, the support faces being placed in line with the upper horizontal faces of said conductors.
 9. Extraction device according to claim 7, characterized in that said frame also includes fairing which delimits the space in which the unit including the wedge and the means of gripping the wedge must move after said wedge has been extracted and which provides protection for operators working near said extractor.
 10. Extraction device according to claim 1, including an intermediate hollow part provided with a horizontal support face directed downwards and in which the body of the at least one jack is interdependent, via said part intermediate hollow part, with said the horizontal support face, the upper horizontal face of each conductor being in line with said horizontal support face when said device is positioned for the extraction of said wedge.
 11. Extraction device according to claim 10, in which the body of the at least one jack has a lower horizontal face which is in contact with the upper horizontal face of said intermediate part when the extraction device is placed on said conductors in order to extract said wedge.
 12. Extraction device according to claim 10, in which the stem of the at least one jack is hollow, passing right through via an axial bore through which an axle interdependent with said means of gripping of the wedge can slide.
 13. Extraction device according to claim 12, in which said axle interdependent with the means of gripping is provided with a shoulder which serves as a stop for the axial movement of stem, so that, when said at least one jack is operated, stem is entrained upwards, the end of said stem comes into contact with the shoulder of said axle, so that said at least one jack is configured to exerts an upwards force on said gripping device.
 14. Extraction device according to claim 12, in which said means of gripping the wedge is fixed to a lower end of the axle, and wherein the axle is an extension of the piston stem of the actuator.
 15. Extraction process for short-circuiting wedges used when switching in an electrolytic cell comprising removing a short-circuiting wedges which was inserted between first and second conductors to take said electrolytic cell off line, the first conductor being associated with a cathode assembly of said cell and the second conductor being associated with a cathode assembly of an adjacent upstream cell, the first and second conductors each having at least one upper horizontal face and a substantially vertical face, the substantially vertical face of the first conductor being placed opposite the substantially vertical face of the second conductor, the two substantially vertical faces delimiting an air-gap designed to receive said short-circuiting wedge, said wedge including two substantially parallel faces, which converge slightly towards a bottom of said wedge when said wedge is placed so as to occupy said air-gap, said process being characterized in that an extraction device is used for removing the wedge, the extraction device including a means of gripping said wedge, wherein said device includes at least one jack directed vertically and comprising a body and a piston associated with a piston stern, wherein: a) one of said body or said stem is interdependent with at least one horizontal support face which is directed downwards and laid out so that, when said extraction device is placed above said wedge to extract the wedge, the upper horizontal face of each of the first and second conductors is in line with the horizontal support face, and b) the other of said stem or said body is connected to said means of gripping said wedge, so that, when said at least one jack is actuated to extract the wedge, said at least one jack exerts opposing forces on said first and second conductors and said wedge, tending to separate the first and second conductors and the wedge. 